Radiant solar energy collecting apparatus in which solar energy is collected and concentrated on a solar energy receiver are well known. Such apparatus is used for electric power production for example in solar thermal power stations where a liquid or gas heated by solar energy is converted into steam or a vapour which is used for generating usable energy. The solar energy concentrators for use in such apparatus may be of various designs. For example, concentrators may be of a parabolic trough or dish design in which a curved parabolic trough or dish concentrates received solar radiation onto an absorber or receiver typically in the form of a pipe or other target containing a heat transfer working fluid. The parabolic trough concentrators may also be of a composite form and comprise for example a plurality of reflectors which may be planar or of a curved configuration. The heat transfer working fluid passes through the absorber or receiver and is heated or superheated and used to drive an engine or turbine. For example, where the working fluid is water, water is converted into superheated steam which may be supplied to a steam turbine. To enable sufficient power to be generated, a solar thermal power station may have many parabolic troughs or dishes occupying a large area of land.
In other systems known as heliostats, a central tower carries a target through which the working fluid flows and a series of flat mirrors which are mounted to track movement of the sun are provided to focus the sun's rays on the target on the tower to heat the working fluid which may then be used for driving an engine.
In my International patent application No PCT/AU99/00140, I disclose radiant energy collecting apparatus which includes a platform assembly floating on a body of liquid typically water usually contained in a reservoir. Reflectors of a solar concentrator in a Fresnel configuration are supported on the top side of the platform assembly to concentrate solar energy onto a secondary concentrator which concentrates the energy on a solar energy receiver usually comprising tubes through which a heat transfer fluid flows. The heat transfer fluid may be water which is converted into steam when the receiver is exposed to the concentrated solar energy and the steam superheated for supply to a steam turbine which can drive an electrical generator for the supply of power. For efficiency of operation, it is preferred that exhaust steam from the steam turbine be condensed into water and the water then reused as the working fluid in the system.
Various different designs of condenser are currently used for condensing steam into water including water cooled condensers and air cooled condensers. A particular disadvantage of water cooled condensers is that it is necessary to have a supply of water for cooling the condenser and absorb the heat of the steam. Further water cooled condensers tend to be of a relatively complex construction. Where water is required for use in a steam condenser, a design which requires water for condensation or cooling may conflict with the location of solar thermal plants. For example, such plants are often located in remote areas such as desert areas where although high solar radiation is available, there may be limited water resources. Thus the most efficient location for such a plant may be affected by difficulty in obtaining an adequate water supply. Some authorities also prohibit the use of potable water for such applications.
Water usage may be reduced by using air cooled condensers to convert the steam back into water. Air-cooling of fluids has assumed an increasing importance as compared to conventional water-cooling due to the growing difficulty in obtaining adequate water supplies and to the problem of thermal and biological pollution caused by the use of water. In typical air-cooled condensers, the fluid or vapor to be condensed is caused to flow through rows of finned heat exchange tubes with air being blown by blowers over the tubes and condensate collecting in a common manifold. As air flows between the rows sequentially, more vapour will condense in the first row of heat exchanger tubes than in subsequent rows and thus the condensing ability varies throughout the condenser. Further known air cooled condensers in addition to having a high cost and a large bulk, have a number of further disadvantages in that they cannot cope with variations in load.
It would be desirable therefore if an improved steam or vapour condensing system which was particularly applicable to radiant solar energy collecting apparatus was available.